1. Field of the Invention
The present invention relates to signal attenuation; and more particularly, a high power selective signal attenuator and method of attenuation.
2. Description of Related Art
Analog-to-digital converters (ADCs) have a dynamic range of operation. The dynamic range is defined as the range from a minimum signal amplitude to a maximum signal amplitude (i.e., between a minimum and maximum power level). Analog signals having amplitudes within the dynamic range of an ADC will be converted from analog to digital.
Analog signals having amplitudes below the minimum power level of the dynamic range will not undergo conversion, while analog signals having amplitudes greater than the maximum power level of the dynamic range will overload or saturate the ADC. More specifically, the ADC will clip the amplitude of an analog signal having an amplitude greater than the maximum power level of the ADC""s dynamic range. Clipping the amplitude of the analog signal causes harmonics which distort and corrupt the whole spectrum such that most signals are virtually lost. Consequently, such ADCs are unsuitable for many of today""s communication needs.
The high-power selective signal attenuator according to the present invention isolates high-power signals in the received analog signal spectrum. The isolated high-power signals are then recombined with the received analog signals such that the high-power signals are substantially canceled from the received analog signals. The isolation of the high-power signals is accomplished by coupling the received analog signals onto a feed forward pathway, and attenuating the coupled signals so that high-power signals fall within the dynamic range of an ADC receiving the attenuator""s output. Because the ADC performs the analog-to-digital conversion operation on signals falling within its dynamic range, the output of the ADC substantially represents the high-power signals in the received signals. The digital signals are then digital-to-analog converted and amplified by an amplifier, which compensates for the attenuation caused by at least the attenuator. The resulting signals are then combined 180xc2x0 out of phase with the received analog signals so that the high-power signals are substantially canceled from the received analog signals.
The attenuation performed by the attenuator in the high-power selective signal attenuator is dynamically controlled by monitoring the output of a primary ADC receiving the output of the high-power selective signal attenuator. As the primary ADC approaches saturation, the attenuation level is increased. As the primary ADC falls further from saturation, the attenuation level is decreased. In this way, the maximum amount of information can be converted by the primary ADC without placing the primary ADC in saturation.